This invention relates generally to semiconductor memories, and more particularly to a system and method for monitoring memory content of a memory cell.
One type of memory utilizes a phase change material that may be, in one application, electrically switched between amorphous and crystalline states, or between different detectable states across the entire spectrum between completely amorphous and completely crystalline states.
The operation of a phase change memory (PCM) is based on a resistance change caused by the different states of the phase change material. Typical materials suitable for the phase change material include, but are not limited to, various chalcogenide glasses, such as GeSbTe. The advantages of phase change memories include high write throughput and single-bit random write access.
When the memory is set in either a crystalline, semi-crystalline, amorphous, or semi-amorphous state having a respective resistance value, that state is retained until reprogrammed, even if power is removed. The state is retained because the programmed resistance represents a phase or physical state of the material (e.g., crystalline or amorphous). The state of the phase change materials is thus generally non-volatile.
A first low resistive state, i.e. crystalline state or semi-crystalline state, is achieved by a small power being applied to the memory compared to the second state, i.e. amorphous state or semi-amorphous state, where a high power pulse is used to melt and quench the material into an amorphous state. It is possible to program the cell into mid-level states by application of medium power levels.